Many apparatuses, movable sections of which are often used in a circumstance (for example, a field of mechanical processing) exposed to water-soluble coolants such as water-soluble cutting oils, solvents or chemicals like limit switches used for position detection of a moving object or for detection of an operation limit or safety door switches for detecting whether or not a mechanical guard or cover is closed, are present.
In such an environment, it is necessary to select a constituent material of a sealing member according to usage environment since degradation and swelling of the sealing member may take place, and conventionally, an NBR (acrylonitrile-butadiene rubber) or a fluororubber, which has excellent oil resistance and chemical resistance, is used. For example, in Patent Literature 1, there is disclosed a technology in which a sealing property against chemicals is secured by providing an O-ring made of a fluororubber between a bearing and a housing and a sealing property against sea water is secured by providing an O-ring made of a nitrile rubber.
Further, since an environmental gas in the field of mechanical processing may contain ozone, the degradation of the sealing member due to ozone becomes a problem when the sealing member is used in a circumstance where much ozone exists. It is disclosed in Patent Literature 2 that a rubber composition including a highly saturated rubber having a specific iodine number, a functional group-containing lube oil and a functional group-containing thermosetting resin has ozone resistance.